Vulcanized natural rubber is widely used in anti-vibration systems, such as automotive engine mounts, because of its excellent strength, fatigue resistance, high resilience and low level of strain sensitivity particularly at low temperatures. It is and has been the elastomer of choice for the majority of applications involving high stress and cyclic flexing. Unfortunately, vulcanized natural rubber tends to degrade when it is used in high temperature environments (>100° C.) and the temperatures in today's engine compartments are increasing in order to improve engine efficiency, with an industry target of at least 150° C. mentioned. With the industry driving to improve engine efficiencies, vulcanized natural rubber mounts may be more susceptible to early degradation and part failure.
To address the problem of vulcanized natural rubber thermal degradation, heat shields have been described, for example, in US Pat. Appl. No. 2006/0138300. Coatings have also been applied to vulcanized natural rubber to reduce their thermal degradation such as described in U.S. Pat. No. 6,709,758. Crosslinking modification and saturation of the double bonds have also been used to reduce the thermal degradation of vulcanized natural rubber, but these invariably have led to substantial reduction in desirable dynamic properties particularly at lower temperatures. Additives such as reversion modifiers and antioxidants have also been used such as described in Accelerators and Reversion Modifiers for Natural Rubber (Dr. Arie J. de Hoog, Natuurrubber 9, December 1997). Unfortunately, these methods suffer from reduced dynamic properties, complexity, increased weight, and limited improvement at higher application temperatures (i.e., desired underhood temperatures).
From the above, it would be desirable to provide a vulcanized natural rubber having similar dynamic properties to a vulcanized rubber using standard sulfur vulcanization methods that realizes improved thermal degradation properties and avoids one or more problems of the prior art such as those mentioned above.